void mainImage(out vec4 fragColor,in vec2 fragCoord){
    vec3 color1 = vec3(1.0,0.0,1.0);
    vec3 color2 = vec3(1.0,1.0,0.0);
    vec3 color3 = vec3(0.0,0.0,1.0);
    vec3 color4 = vec3(1.0,0.0,0.0);
    //iResolution shaderToy 内置变量
    //window.innerWidth
    //czm_viewport.zw
    if(fragCoord.x < iResolution.x *0.25){
        fragColor = vec4(color1,1);
    }else if(fragCoord.x >= iResolution.x*0.25 &&fragCoord.x < iResolution.x*0.5){
        fragColor = vec4(color2,1);
    }else if(fragCoord.x >= iResolution.x*0.5 &&fragCoord.x < iResolution.x*0.75){
        fragColor = vec4(color3,1);
    }else{
        fragColor = vec4(color4,1);
    }
}